FIG. 5 is a plan view illustrating an ink ribbon 4 used in a thermal transfer printer. A thermal transfer printer capable of printing color images uses, for example, the ink ribbon 4 shown in FIG. 5, on which color ink regions of yellow Y, magenta M and cyan C and an overcoat OP region are repeatedly arranged in the same order in its longitudinal direction. While transporting the ink ribbon 4 in the direction of arrow A1, the printer sequentially transfers the color ink of yellow Y, magenta M and cyan C onto elongated receiver paper 10 to print an image I, and further transfers thereon the overcoat OP for enhancing light resistance and abrasion resistance, thereby forming a protective layer on the surface of the image I. After that, the printer transports the paper 10 in the direction of arrow A2 and cuts its leading edge, and further transports the paper 10 in the same direction and cuts the trailing edge of the image I, thus discharging the printed matter out of the printer.
During the transfer, the thermal transfer printer causes the thermal head to apply heat to the ink ribbon from the side opposite to the front side on which the ink layer (colorant layer) is provided. Of such ink ribbons, those which include a back layer made of a heat-resistant resin on the back side, which comes into contact with the thermal head, for enhancing heat resistance are known, as are those which include in the back layer a lubricant and an inorganic or organic particulate filler for reducing friction between the thermal head and the ink ribbon (see Patent Literature 1 and 2, for example).
FIG. 6 is a cross-sectional view of the ink ribbon 4. The ink ribbon 4 includes a base 41, a colorant primer layer 42, a colorant layer 43, an overcoat layer 44, a back primer layer 45 and a heat-resistant lubricating layer 46. The base 41 is placed at the center in the thickness direction of the ink ribbon 4. The colorant primer layer 42 is formed on one side of the base 41, while the back primer layer 45 is formed on the other side of the base 41. The colorant primer layer 42 corresponds to the front side which comes into contact with the paper 10, while the back primer layer 45 corresponds to the back side which comes into contact with the thermal head. The colorant layer 43 is a color ink (colorant) layer of yellow, magenta and cyan, and is formed on the colorant primer layer 42, together with the overcoat layer 44. The heat-resistant lubricating layer 46 is a layer containing a lubricant, a binder resin and a suitable filler, and is formed on the back primer layer 45.